Electrohydraulic flow control apparatus



Aug. 17, 1965 c. E. ADAMS ELECTROHYDRAULIC FLOW CONTROL APPARATUS Original Filed April 4. 1961 INVENTOR. CECIL E. ADAMS BY wa w M fia/x4 irmemr:

United States Patent 3,29%,832 ELECTRGHYDRAULIC FLOW CUNTRGL AIPARATUS Cecil E. Adams, Columbus, Ohio, assignor to American Brake Shoe Company, New York, N.Y., a corporation of Delaware Original application Apr. 4, i961, Ser. Nos 1%,753, new Patent No. 3,159,178, dated Dec. 1, 1964. Divided and this application Oct. 24-, 1963, Ser. No. 318,676

6 Claims. (Cl. 137-117) This invention relates to apparatus for adjustably controlling the rate of flow of hydraulic fluid under pressure. More particularly, the invention relates to electrically controllable apparatus for adjustably regulating the rate of flow of hydraulic fluid under variable pressure conditions. This application is a division of my copending application Serial No. 100,753, filed April 4, 1961, now Patent No. 3,159,178.

Devices for regulating the flow of hydraulic fluid have utility for a wide variety of purposes. For example, such devices are commonly employed to permit only a fixed number of gallons of fluid per minute to flow to a hydraulic motor, thereby maintaining the speed of rotation of the motor at a fixed number of revolutions per minute. As another example, it is often desirable to admit fluid at a constant flow rate to the cylinder of a hydraulic ram so that the ram will advance at constant speed regardless of variations it may encounter in the resistance presented to it by a work piece.

While there have heretofore been available flow control devices which permit adjustment or change in the volume of flow which they permit to pass in unit time, it has usually been necessary to make such adjustments manually, as by loosening a lock nut, changing the relative position of an orifice-forming element, and then retightening the nut. For obvious reasons, it has been dimcult to make such adjustments remotely. Moreover, it has been diflicult quickly to set previous flow control devices to maintain the flow rate at any preselected numerical value. For example, if it is desired, say, to maintain a flow rate of 4 gallons per minute to a hydraulic motor, the flow control apparatus must usually be set so that the flow rate will approximate the desired value. With the apparatus thus set, the actual flow must then be measured and the setting of the apparatus inched to a better approximation of the desired rate. That this type of adjustment has been difficult to effect remotely can also be appreciated.

In contrast to such past devices, this invention is directed to flow control apparatus which is electrically controllable and by which the flow rate may be set at any desired value quickly, remotely, and accurately.

In accordance with one embodiment of the invention, the rate of flow of fluid under pressure to a work load may be set at any desired value within a preselected operat ing range simply by regulating the current supplied to an electromechanical control element. This flow rate will thereafter be maintained regardless of variations or fluctuations either in the pressure of the fluid supplied to the flow control apparatus or in the resistance encountered at the work load.

Broadly speaking, in a main aspect, the flow control apparatus of this invention includes structure forming a main orifice, structure forming a pilot or trimmer orifice, fluid passageways through which fluid under pressure is supplied to the respective inlets of the main and pilot orifice structure, and pressure differentially operated means whereby the pilot or trimmer orifice structure is rendered eliective to control the total flow of fluid through the flow control apparatus to an output or load conduit. More specifically, in a preferred form the invention comprises a main flow orifice assembly, a pressure regulator assembly, and a trimmer or pilot valve. The main flow orifice assembly includes a body having an inlet port and an outlet port and structure forming an adjustable or variable orifice between those ports the area of which can be varied. The pressure regulator assembly maintains a constant pressure differential or pressure drop between the pressure of fluid at the inlet and outlet ports of the main flow orifice assembly. The trimmer or pilot valve includes a body having a bore, an inlet. port and an outlet port, a movable valve member for esetablishing a pressure drop between the inlet and outlet ports, and an electromechanical transducer for actuating the valve mem her which delivers a substantially constant force for a given electrical input thereto in a direction tending to close the pilot valve. A fluid passageway including a flow restrictor communicates between the inlet port of the main flow orifice assembly and the inlet port. of the trimrner or pilot valve, and other means interconnect the pilot valve with the main flow orifice assembly in such manner that the pilot valve is rendered eiiective to control the total flow delivered by the fiow control apparatus to an output or load conduit.

These and other aspects of the invention may best be described by reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a preferred fiow control apparatus in accordance with the invention; and

FIGURE 2 is a schematic diagram of a hydraulic system incorporating a three-port electrohydraulic flow control apparatus for operating a fluid motor, including a cross-sectional view of an electrohydraulic pilot valve, a schematic view of an electronic circuit for controlling the operation of the pilot valve, and a cross-sectional view of a flow metering mechanism responsive to the pilot valve for regulating the flow of fluid to the work load.

In FIGURE 2 of the drawings there is shown a system in accordance with a preferred embodiment of the invention for supplying hydraulic fluid under pressure to a work load at a controlled rate. The operation of this system is controlled by an electrical input supplied to it. It can be set, by closing an appropriate switch, to provide any or" a number of preselected operating ranges over each of which the rate of flow can be either gradually varied or set at any value in the range simply by adjusting a variable resistor.

Broadly speaking, the system of FIGURE 2 includes a source iii of fluid under pressure, a work load iii. which for purposes of illustration is taken to be a fluid motor, a flow metering mechanism or assembly 12 connected between the source of fluid iii and the work load ll. for controlling the flow to the load, an electrically operated pilot valve 13 which governs the fiow rate maintained by the flow metering assembly 12, and an electric circuit lid for operating and controlling the pilot valve 13.

Referring to the figure in detail, the source of fluid pressure it is conventional and may comprise an electric motor to driving a hydraulic pump 17'. The pump receives hydraulic fluid from a tank 13 through a conduit 2d, and discharges fluid under pressure into a conduit 21. Thi conduit 21 is connected to tank 18 through a relief valve 22 and a conduit 23. These elements 1643 will be understood to represent a conventional source of fluid under pressure by which the work load ll is operated.

A high pressure conduit 24 is connected from the relief valve 22 to the inlet port 25 of the flow metering assembly 12. A conduit 26 connects the load port 27 of the flow metering assembly 12 to the fiuid motor il, a conduit 28 connects the low pressure side of the fluid motor ii to the tank 18, and another conduit 39 connects the tank port 31 of the flow metering apparatus to the tank 13. Thus, it will be seen that the arrange ment described is of the meter-in type, in which the flow control mechanism is in series with (i.e., is connected directly to) the work load, and is further of the threeport type, in which the flow metering assembly diverts to tank that portion of the flow entering its inlet port which is in excess ofthe flow which is to be directed to the work load. As will be described more fully hereinafter, the function of the pilot valve 13 is to determine, in ellect, what portion of the high pressure fluid entering the flow metering assembly 12 shall be metered to the -fluid motor llll through conduit 26 and what portion shall be diverted to the tank 18 through conduit The flow metering assembly FIGURE 2 The flow metering assembly 12 is contained in a body 33 in the form of a block which is provided with two spaced, parallel vertical bores 34 and 335. Bore 34 contains elements which cooperate to form pressure compensating or regulating means, while bore 35 contains elements which cooperate to form a variable orifice by which the rate of flow of fluid to the load port 27 of the flow metering assembly is directly controlled or metered.

The elements contained Within bore 34 include a cylindrical element 36 having spaced circumferential grooves 37, 33, and 39 formed therein, which is inserted into one of the open ends of bore 34 and is retained therein by a snap ring all. The cylinder 36 is sealed to the bore by an O-ring contained within groove 37 which is adjacent snap ring 41. Cylinder 36 also includes a central axially extending bore 42; which extends upwardly toward but not through its upper end which is connected to grooves 38 and 39 by passages or ports 43 and 44 respectively.

A compound piston element 46 is also contained within bore 34 and includes a piston head 47 of diameter equal to that of the bore and a small diameter shank 4 25 which extends to and reciprocates within bore 42- of cylinder 36. This shank ts is provided with a circumferential groove t and a pair of lands 51 and 52. Land 51 functions merely as a guide or hearing for the compound piston 46 and never closes port 43. Land 52 cooperates with port 44 to form a valve for controlling the flow of fluid through port 44 in accordance with the vertical position of the V sharp upper peripheral edge of the land which is adjacent groove 5%. The compound piston 46 is provided with a vertical bore 53 which extends downwardly from its upper end and communicates through a lateral drilling 54- to the upper side of the piston head 47.

The piston 46 is urged upwardly to the position shown in FIGURE 2 by a spring 55 which abuts the piston head 47 and a block 56. Spring 55 is a low rate spring; that is, the force it supplies when compressed is relatively independent of the degree of compression it has undergone. The block 56 is inserted into the other open end of bore 34, sealed by an O-ring 57, and is retained in the bore by a snap ring 58. The block 56 forms an abutment which limits the downward movement of the piston in bore 34. The chamber formed in the bore between the upper face of the piston head 47 and the adjacent end of cylindrical element 36 is connected with groove 39 by a passage as formed in the cylindrical element and extending from port 44 to the bottom of element as.

The other bore (35) in body 33 contains elements which form a variable orifice for metering the flow to load port 2'7. As can be seen from FIGURE 2, the elements contained in bore 35 are preferably generally similar to those contained within bore 34, with the exception that they are reversed or upside-down with respect to those of bore $4. Thus, bore 35 is provided with a cylinder 61 having spaced circumterentital grooves 62, 63, and 64, and is sealed to and retained within bore 525 by an O-ring in groove 64 and a snap ring 65 at its lower end. This cylinder 61 is provided with a downwardly extending axial bore as, ports 69 and 7d connecting grooves 62 and 63 respectively to this bore 6%. A compound piston element 72, reversely oriented with respect to the corre sponding piston as in bore 34, is slidably received in bores sf 35 and 63. This piston 72 has a head which is sea iingly slidable in bore 35 and shank 7d wlich extends into and reciprocates within bore 63. This shank M is provided with a circumferential groove 75 and lands "K and '77. Land 76 cooperates with port 69 to form a valve for metering the flow of fluid to load port 2'7 in accordance with the-vertical position of the sharp lower peripheral edge of land '76. Land '77 functions merely as a guide and never closes port 7t An upwardly extending small diameter bore '79 connects the lower end of shank 74 of compound piston 72 with the underside of piston head 73 through a lateral drilling The piston 72 is urged downwardly in bore 35 by a high rate spring 81, the force delivered by which depends sharply on its relative compression. 1 his snring $1 abuts piston head 73 and a block $22 which is sealed an retained within bore by an O-ring and snap ring respectively. A bore 36 connects the chamber formed by the wall of bore and groove 3% of cylinder 36 with the control chamber formed by the wall of bore 35 and upper face of piston head '73; this latter chamber is connected through tank port Ell to tank conduit A bore connects the chamber formed by tne wall of bore 3 and groove 39 in cylinoe 36 with the corresponding chamber of bore 35 formed within cylinder 61. A third bore reflects the pressure of iluid in the outlet conduit 26 to the chamber in bore 34 which is below the lower face of piston head 4-7. Pilot valve ports 239 and 9d are formed in body 33 respectively entering the chamber in bore 35 bounded by groove 62 and the control chamber between the lower face of piston head 73 and the upper end of cylinder til.

The pilot valve of, FIGURE 2 As previously noted, the setting of the flow metering apparatus 12 is controlled by an electrohydraulic pilot valve 13. In FIGURE 2, pilot valve 13 is shown separately from the flow metering apparatus 12 for clarity, but in practice it is preferred to mount the pilot valve physically adjacent or on top of. the flow metering apparatus in the manner shown in FIGURE 1. a

The pilot valve 13 is housed in a body comprised of two elements $5 and 9a which are connected by screws not shown. The lower body element 9-6 is provided With a fiat bottom surface for mounting atop a block 97 which, as explained, can in practice he contiguous with the flow metering apparatus 12. An O-ring ill]; in a groove in the lower surface of body element as forms a seal with the top surface of block 97. An inlet passageway d8 extends from port 3) of the fiow metering apparatus 12 through a restricted orifice 99 to the upper surface of block 9? where it forms an inlet or control port 1%. A bore Hi2 enters bore 98 downstream of orifice 99 near inlet port ll lll and is connected to a conduit 1% leading to pilot valve port as of the how metering assembly. An outlet passageway l thiopens on the top surface of block 9! at a position spaced from inlet port Tilt) and is connected to tank conduit 3h.

The lower body element Q6 of the pilot valve is provided with a stepped vertical bore MS which is axially aligned with port rec in block 97 and which is enlarged at its lower end to communicate with the outlet passageway 1%. This bore N5 is divided into two chambers, one a wet chamber res and the other a dry chamber M7, by a seal and guide assembly 168 and a diaphragm 1%? is the form of a flexible boot. Bore res is joined below this boot M9 by a horizontally extending bore ill which is partially closed by a breather or vent plug 112. Body element 96 is also provided with a passageway 11?) through which pass insulated wires connected to the electric coil lid and thermistor or" an elcctro-rnechanical transducer assembly contained in body member 95.

A movable valve element or poppet lid is contained within the wet chamber and is mounted on the lower end of an operatin rod 119 which extends through the its upper end is abutted by an adjusting screw lli 'l which seal and guide assembly 1%. This valve element 118 :has a large diameter head 120 provided with a downwardly extending peripheral flange 121 which tapers downwardly to a relatively sharp edge. Above head 12d, valve element 118 is provided with a shank of small diameter in which is formed a cup 122 in which the lower end of openating rod 11? is loosely received. Together with port 1% of bore 98, poppet 113 forms a valve assembly which acts on fluid flowing from inlet port 1110 to outlet passageway 104 to create a back pressure at port 100. The particular construction shown is preferred for this valve because it is self-cleaning and presents a relatively large area to the pressure of fluid at port 1136, but it is contemplated that other suitable constructions may be employed.

The seal and guide assembly 168 includes a circular disk 123 having cylindrical outer walls. This disk is inserted into that portion of bore 165 which cooperates in forming the dry chamber 107 against the shoulder therein which is adjacent the upper end of wet chamber 106. An O-ring seal 124 which is contained Within an annular groove in the bore 105 adjacent the shoulder engages the cylindrical outer Wall of the disk 123 and seals it to the bore. The disk 123 is retained against axial movement in bore ltlS by a washer and a snap ring, the latter being seated in an annular groove in the wall of bore 1&5. Disk 123 is also provided with .a central axial bore through which operating rod 119 extends. An O-ring 126 is inserted in a groove adjacent the top of the bore in disk 123 through which the operating rod extends and is held therein by the bottom surface of the washer. The rod 119 does not contact either the disk 123 or the washer and is supported solely by O-ring 126. By these means rod 119 is sealed with guide assembly 198 in a substantially frictionless manner, because the axial motion of rod 119 is generally in the nature of not more than two thousandths of an inch, under which conditions O-ring 126 forms an anti-friction bearing, since it tends to roll upon the rod as the latter is reciprocated.

The upper end of dry chamber 107 is closed by the previously mentioned flexible boot 1129 which is inserted into bore Hi5 against a shoulder therein. An expansible type coil spring 127 retains boot 109 in bore 1%, and the boot is provided with a thickened elastic central portion having a bore which surrounds and sealingly grips a nonmagnetic brass shaft 128 which carries rod 119.

Body element 95 is cast of an non-magnetic material such as aluminum, and is bored to receive a core 129 in which the coil 11d and thermistor 115 of the transducer assembly are housed. Core 129 and an armature disk 13% which is positioned above it are preferably formed of material which has high magnetic permeability and low hysteresis such as an ingot iron. Core 129 is a cupshaped cylinder having side walls 131 which provide magnetic poles and a hollow center post 132 which also provides magnetic poles. Coil 114 is embedded in an insulating plastic material in the core 12%, while thermistor 115 is embedded in the same plastic material in a notchlike opening formed in the bottom of the core 12a. The outside diameter of the core 129 is such as to establish a close slidable fit with bore in body element 95, and the core is provided with a peripheral flange 133 which abuts a shoulder on body element 95. Flange 133 of core 129 is clamped to body element 95 by a snap ring in a groove in body element 95.

The electromagnet above described including core 129 and coil 114 operates an armature including disk 139. This disk has a hollow hub 135 into which a tube 136 of nonmagnetic material is pressed. The armature disk 13% extends over the outside magnetic poles formed by the side walls 131, and tube 136 extends freely through the center post or poles 132 of core 129. The armature disk 136 does not contact body element 95. Shaft 128 fits snugly but axially slidably within tube 136 of the armature and crease in its resistance.

is threaded into the upper end of tube 135 and which is provided with a locking nut 138. An externally threaded hollow plug 14% covering screw 137 and nut 138 is threaded into body member 95. Rotation of core 129 and armature disk 131 with respect to each other and body element is prevented by a nonmagnetic pin 141 which extends through disk 130 into aligned openings in body element 95 and core The opening in the armature disk through which pin 141 extends is of a diameter larger than that of pin 141 so that should disk 13d contact the pin during operation of the device there will be substantially no frictional resistance between them. Pin 141 extends through disk 130 to hold it against rotation during adjustment of screw 137 and nut 138.

It is to be understood that while the above described pilot valve comprises a preferred construction, the principles of the invention are not limited to that specific valve and other specific types of electrically operated pilot valves are within the scope of the invention.

As will be explained, the armature assembly of the transducer is electromagnetically urged in .a direction to close valve 1%, 118 and is urged in the opposite direction by fluid pressure acting upon the bottom surface of the head 12% of valve element 118. When this fluid pressure overcomes a predetermined electromagnetic force of the transducer, the valve will be opened to a position Whereat the fluid forces acting upon element 1T8 exactly counterbalance the counteracting electromagnetic force. Should the fluid forces acting upon valve element 118 vary in even the slightest degree, then the opening through the valve ltitl, 1. .8 will be varied to maintain a desired pressure drop between inlet port 1% and outlet bore 104. It has been found during repeated tests and in the actual operation of pilot valve 13 that the valve does not tend to hunt when the electric current supplied to its coil or the pressure conditions in inlet port 1% are changed, and that the valve responds quickly even to sudden changes in electric current and/or pressure.

The force exerted by an electromagnet on an armature spaced from it is inversely proportional to the square of the distance between the armature and the poles of the magnet for a constant magnetomotive force. For this reason the coil 11 i and core 129 of the transducer are preferably made large in order that there may be a wide air gap between the armature disk 13b and the poles 131 and 132, whereby in that range (ti-.602 inch) in which the armature moves, the force acting upon the armature will remain substantially constant for any given magnetomotive force produced by the coil 11d, and the transducer will deliver a substantially constant force Within its predetermined stroke range in response to that magnetomotive force.

Coil 114 will tend to heat up under typical conditions of operation, which normally is accompanied by an in- Since this increase in coil resistance would diminish coil current and thereby cause the electromagnetic flux of the coil to decrease, thermistor 115 is preferably included in series with coil 114 by connection with coil lead 142 A resistor R is connected in parallel with thermistor 115 between leads 142 and 14d. The combination of coil 114, thermistor 115, and resistor R presents a combined resistance between coil leads 14-3 and 144 which varies only a minimal amount with temperature, so that the overall resistance through which the pilot valve current passes is substantially constant. The combination of resistance elements will thus be understood to be equivalent to a temperature constant resistance.

The electrical control circuit 0] FIGURE 2 FIGURES 2, 3 and 5 each show a preferred electrical circuit 14- whereby the pilot valve 13 may be accurately controlled to maintain any flow within a desired operating range. It is to be unders ood tha t hile the circuit shown Z 13, the valve may be used with any other suitable source of electrical power.

The circuit 14 is designed to operate on conventional 110 volt, 6O cycle alternating current, is relatively simple and compact, and enables the operation of the pilot valve to be easily, accurately, and remotely controlled over its entire operating range. The circuit includes a power supply which is shown at the lower left portion of the figure. This power supply provides a regulated or constant direct current output at points and 166. Power supply leads l4! and are connectable to a convcntional source of alternating current not shown.

A resistor R is connected between lead s47 and a junction ltd-ll. A diode D permitting cur c to liOVI to the right, is connected between junction and a second junction 1.51, while revel" y orient t diode B permitting current flow to the lets but not the right, is connected from junction llStl to a junction Condenser C is connected from junction to lead and condenser C is connected in series with c0. "enser C from lead 143 to junction 1.52. Resistor R is connected from junction 1551 to the plate connection 153 of a voltage regulator tube junction is connected by a lca 154- to the cathode connection of tube Vii.

in operation, condensers C and C are charged thro oh diodes D and D on opposite half-cycles of the current, so that a relatively high, fluctuating potcn tends to be established between junctions 151 and 152. The voltage regulator tube Vii regulates this potential so that a lower, substantially constant potential is s plied at points 3 .45 and i l-i5, the former being positive with respect to the latter.

Referring now to the preferred control circuit itself, which appears to the right of the power supply, leads 15% and 15% are connectable to a conventional source of alternating current, as by respective connection to leads 147 and M3. Lead is connected to a variable resistor R which has an adjusta le tap Tap is connected to one end of the primary winding of a transformer T, the other end or the primary being connected to lead 159.

A variable resistor R having an adjustable tap 161 is connected at one end to the power supply at tap er being connected to a junction 152. A variable resistor R having a tap use is connected to the power supply at 146 through a lead Tap 1 53 of resistor 1 a is connected to junction 162, and a condenser C is connected between junction Th2 and lead The secondary winding of the transformer is connected at one end to lead 164 and at the other end to lead The respective taps Lib, 1st and 163 of resistors R and R and R are ganged as shown for simultaneous movement.

lunction 1G2 is connected through a diode D which permits current flow to the right but not to the left, to a lead are Eetween lead res and coil lead 14:: more connected in parallel a number of variable resistors R R R R and R each resistor having a switch SW SW SW SW,;, and SW respectively connected series with it between leads 1 13 and 11115. The t'u these resistors are respectively designated lo), and 176 These taps are preset so that by selectively closing any of switches SW -N current will flow from lead 165 to lead 143 through a resis. r R 3 or" predetermined resistance.

The operation of the pilot valve control circuit 14 may now be explained. When energized, direct current from the power supply flows from positive connection 145 through resistor R to tap loll, through lead 165 to whichever switch SW FNJ has been closed, through the rcsistor connected in series with that switch to lead 143 and coil 114. From the coil, the current flows through parallel-connected thermistor 115 and resistor R to lead 144,

then through the secondary winding of transformer T and lead 164 to negative connection or" the power supply. The magnitude of this current may be varied by adjusting variable resistors R and Ri 'tial in the secondary winding of the transformer I V The application Of an alternating potential to the pri- T induces an alternating potenwhich jis super-imposed on the direct voltage applied to the coil 11 This alternating voltage is applied to the circuit through lead 164, condenser C or tap 163 depending on the position of the tap along resistor R diode D leads 165 and 14?), valve coil 114, through thermistor and resistor R and transformer secondary lead 144.

By reason of the superimposition of the alternating potential or voltage established by the transformer on the direct voltage established by the power supply, the current in coil lll i becomes a modulated or fluctuating direct current which causes the coil flux to fluctuate very rapidly about an average value and thereby minimizes 0r narrows the range of hysteretic variation of the core material. By adding an alternating potential or voltage component to the direct voltage, the valve response variation due to hysteresis of the core 129 may be greatly reduced, to as little as plus or minus one half of one percent or less. The overage direct voltage establishes the setting of the valve, while the alternating potential or voltage is effective to minimize the deviation about that setting which is due to the hytsteresis of the core material of the transducer. Because it is desirable, in connection with the particular pilot valve 13 shown for purposes oiillustration, to use a relatively large alternating potential or Voltage with a low direct current component of total current and to use a relatively smaller alternating poten tial or voltage with a higher direct current component, the resistor R R and R are ganged as shown so that the modulating voltage will be automatically'reduced as mary leads of transformer the direct voltage is increased. Thus, as the taps are moved downwardly on the resistors the direct current is Operation of the system of FIGURE 2 With this description in mind, the operation of the hydraulic system of FIGURE 2 may be described.

Fluid under pressure from conduit 24 enters the flow metering assembly 12 through inlet port 25. The fluid exerts a downward pressure, through port 44 and passageway as, on the upper face of head 47 of compound piston element as. This same pressure is also applied to the upper end of shank 4 5 through bore 53 which communicates at its lower end with the chamber above the upper face of poston head d7. Thus, the pressure of fluid in port 44 is applied downwardly over an area equal to the area of the lower face of piston head 47. Depending upon the pressure of fluid in the chamber beneath piston head 47, which together with spring 55 exerts a counteracting upward force, piston as is moved downwardly in bore $2 to a position at which the valve formed by port 44 and land 52 is open, so that a portion of the fiow in conduit 24 is directed through groove 5b to port 43, and then through groove 38 and bore 8-5 to tank port 31 and tank 18 through conduit 3-1 It is the axial position of the sharp upper end of land 52 with respect to port 44 that determines, under given pressure conditions, the proportion of inlet flow which will be returned to tank and the proportion which will be applied to the variable orifice mechanism in bore 3".

As previously indicated, when the ystem is in operation a constant flow is maintained at the load port 27 of flow metering assembly 12 regardless of pressure fluctuations either at inlet port or at load port 27. It is the pressure compensator or regulator mechanism in bore 34 which is responsible for this action and it is the variable orifice in bore 35 that directly meters the volumetric flow to the load H. A main function of the pressure compensator is to insure that a constant pressure differential is always maintained across the variable orifice between bore 88 and outlet port 27.

Fluid enters the variable orifice mechanism from bore 88 to groove s2 and port 69. With the compound piston 72 in the position shown in FIGURE 2, land 76 closes port 69 and no fluid is permitted to flow to load port 27. However, when the balance of forces acting on piston 72 is such that the piston is moved upwardly so that valve 69, 75 is open, port 659 communicates with groove 75, and fluid passes through groove 75, port 70, groove 63, load port 27 and conduit 26, and is returned to tank 13 from the motor 11 through conduit 28'. It is the pilot valve 13 which determines the balance of forces acting on the opposed control surfaces of compound piston 72, as will now be explained.

Assume that the balance between the downwardly acting force of the transducer and the upwardly acting hydraulic force on valve element 118 is such that valve 100, 118 is partially open. With the valve 100, 118 in this attitude, fluid flows from groove 62 of the variable orifice mechanism to pilot port 89, through conduit 98 to inlet port Hit and into wet chamber N6, past the sharp flange 121 of poppet 113 to outlet passageway 104 which is connected to tank conduit 30. Restricted orifice 99 in here 58 limits the volume of fluid thus passing through the pilot valve to tank.

Valve till), 11% restricts the passage of fluid from port 1% to outlet passageway 164- so that a back pressure is established at port 100. The pressure at port 1% is applied through bore me to the control surface comprised by the underneath side of piston head 73. This pressure is also applied through drilling 3t and bore 7% to the lower end of shank '74. The pressure of fluid in the control chamber above piston head 73 is at all times substantially equal to tank pressure because that chamber communicates directly with tank 18 through port 31 and conduit 30. Only the high rate spring {t1 acts to oppose the up ward force of the fluid pressure on the underside of the piston head 73, and this spring provides a downwardly acting force on the piston head which increases as the piston is moved upwardly. Therefore, the piston is moved upwardly, releasing fluid through port 69, to a position at which the downward force of spring 81 balances the upward force of the fluid on the underside of piston head 73. Thus, from what has been said, it will be seen that the pressure drop across valve 1%, 118, determines the area of the orifice formed by valve elements 69, 76. Since the pressure drop across valve M0, 113 is controlled by the current applied to the pilot valve, merely by controlling the magnitude of that current the area of this orifice, and consequently the flow through it to load port 27, can be controlled.

The pressure at load port 27 is reflected in the chamber beneath piston head 47 through transverse bore 87. This pressure, together with the force of spring 55, acts on piston 46 to cause valve 44, 52 to maintain a constant pressure diflerence across the variable orifice 69, 76, whereby a constant flow through the orifice will be maintained for any given position of land 76 with respect to port 69. If, for example, the pressure at port 27 rises due to resistance encountered in the work load, this high pressure is reflected backwardly across orifice 69, 76 to port 44 and momentarily causes a greater flow through valve 44, 52 to tank, so that less fluid passes through the orifice 69, 76. Since less fluid is passing through this orifice, the pressure drop across it becomes smaller. A relatively larger force is thereby applied to the underside of piston head 47, so that piston 46 is urged upwardly, reducill ing the flow to tank and directing a greater flow to orifice 69, 76, so that the original pressure drop across that orifice is re-established and the desired flow t0 the motor is maintained.

When no current is applied to the valve coil 114, the valve 1%, H3 is wide open; substantially no pressure drop occurs across it, and the pressure in bore tea is substantially tank pressure. Spring 81 then forces piston '72 to the position shown in FIGURE 2, in which port 69 is closed, and the flow to the fluid motor is cut off. The lower pressure at port 27 is reflected through bore 37 to the chamber below piston head 47, so that the high pressure acting downwardly on the piston fully opens valve 4-4, 52, and all flow is diverted to tank. Thus, for any given current applied to it, the pilot valve 13 will control the flow from the flow control assembly to the output or load conduit as.

The settings of the resistors R R determine the maximum current that can flow in valve coil 1114 upon closure of the corresponding switches SW -SW and thus in effect determine the various ranges of flows obtainable from the system. For example, with switch SW closed, a relatively large maximum current can flow to coil 11d. Since maximum valve current corresponds to maximum how in conduit 26, closure of switch SW will permit the highest maximum flow, and the widest flow range. The particular flow actually permitted by the pilot valve in that range depends upon the setting of the ganged resistors R R and R By setting these resistors to present maximum resistance to the DC. component of current, substantially zero flow will be permitted; by changing the resistances Rg-Rg so that smaller resistances to the DC. component of current are presented, larger flows up to the maximum permitted by resistor R are obtained. Alternatively, by closing one of the other switches SW to SW successively smaller maximum currents to the pilot valve 113 are permitted so that successively smaller flow ranges are established.

While I have described a preferred embodiment of my invention, it will be understood that the invention is not limited to the use of the particular flow metering mechanism illustrated, nor the specific pilot valve illustrated, nor the circuit 14 illustrated, and that the invention includes the use of other pressure compensators, variable orifice means, and transducer operated valves and/or circuitry within the scope of the claims which follow.

I claim:

1. Flow control apparatus for maintaining a predetermined rate of flow of fluid under pressure to a work load under variable pressure conditions, comprising, (a) variable orifice means, said variable orifice means comprising a body having a bore therein, an inlet port and an outlet port communicating with said bore at spaced positions, a movable valve member slidable in said bore, said member having a fluid passageway centrally formed therein which cooperates with one of said ports to form a variable orifice regulating the flow of fluid from said inlet port to said outlet port through said passageway, the area of said orifice changin as said valve member is moved axially, said member having opposed surfaces of equal areas presented to two opposed pressure control chambers defined in said bore, both said chambers being isolated from said passageway, inlet port and outlet port, there bein no other surfaces of said member exposed to fluid pressure tending to move said member axially, and elastic means biasing said member in a direction tending to close said variable orifice, (b) pressure compensator means maintaining a pressure differential between fluid pressures at said inlet port and outlet port which is substantially constant for any given position of said member with respect to said body, and (c) electrically controllable means for establishing a pressure differential between tie pressures of fluid in said two control chambers, said electrically controllable r it means having an inlet connected to one of said control chambers and an outlet connected to the other of said two control chambers and to a fluid drain, means including a flow restrictor connecting said inlet to a source of pressure fluid, the fluid force arising from the pressure differential established by said electrically controllable means being the sole pressure diilerential fluid force which is exerted on said movable member tending to move said movable member to vary the area of said orifice.

2. Flow control apparatus for maintaining a predetermined rate of flow of fluid under pressure to a work load under variable pressure conditions, comprising, (a) variable orifice means, said variable orifice means comprising a body having a bore therein, an inlet port and an outlet port communicating with said bore at axially spaced positions, a movable valve member slidable in said bore, said member having a fluid passageway centrally formed therein which cooperates with one of said ports to form a'variable orifice regulating the flow of fluid from said inlet port to said outlet port through said passageway, the area of said orifice changing as said valve member is moved axially, said member having opposed surfaces of equal areas presented to two oppose pressure control chambers defined in said bore, both said chambers being isolated from said passageway, inlet port and outlet port, there being no other surfaces of said member exposed to fluid pressure tending to move said member axialiy, (b) pressure compensator means maintaining a pressure differential between fiuid pressures at said inlet port and outlet port which is substantially constant for any given position of said member with respect to said body, and (c) electrically controllable means for establishing a pressure differential between the pressures of fluid in said two control chambers, said electrically controllable means having an inlet connected to one of said control chambers and an outlet connected to the other of said two control chambers and to a fluid drain, means including a flow restrictor connecting said inlet to said inlet port of said variable orifice means, the fluid force arising from the pressure differential estab lished by said electrically controllable means being the sole pressure differential fluid force which is exerted on said movable member tending to move said movable member to vary the area of said orifice.

3. Flow control apparatus for maintaining a predetermined rate of flow of fiuid under pressure to a work load under variable pressure conditions, comprising, (a)

variable orifice means, said variable orifice means comprising a body having a bore therein, an inlet port and a work port communicating with said bore at axially spaced positions, a movable valve member slidable in said bore, said member having a fluid passageway centrally formed therein which cooperates with one of said ports to form a variable orifice regulating the ilow of fluid from said inlet port to said work port through said passageway, the area of said orifice changing as said valve member is moved axially, said member having opposed surfaces of equal areas presented to two opposed pressure control chambers defined in said bore, both said chambers being isolated from said passageway, inlet port and work port, there being no other surfaces of said member exposed to fluid pressure tending to move sa d member axially, and elastic means biasing said member in a direction tending to close said variable orifice, (b) pres sure compensator means maintaining a pressure diflerential between fluid pressures at said inlet port and work 'port which is substantially constant for any given position of said member with respect to said body, (c) a pilot valve having an inlet and an outlet, means including a fixed flow restrictor supplying fluid under pressure to said inlet, a movable valve element cooperable with a control port for establishing a pressure drop between said inlet and said outlet when fluid under pressure is applied to the inlet of said pilot valve, an electromer2 chanical transducer for actuating said valve clement reiative to said control port to adjust said pressure drop in accordance with an electric signal applied to said trans ducer, and (d) passage means reflecting said pressure drop between the pressures of fluid in said two control chambers, the magnitude of said pressure drop thereby controlling the area of said variable orifice.

t. Flow control apparatus for maintaining a predetermined rate of flow of fluid under pressure to a work load under variable pressure conditions, comprising, (a) ,variable orifice means, said variable orifice means comprising a body having a bore therein, an inlet port and a work port communicating with said bore at axially spaced positions, a movable valve member slidable in said bore, said member having a fluid passageway centrally formed therein which cooperates with one of said ports to form a variable orifice regulating the flow of fluid from said inlet port to said work port through said passageway, the area of said orifice changing as said valve member is moved axially, said member having opposed surfaces of equal areas presented to two opposed pressure control chambers defined in said bore, both said chambers being isolated from said passageway, inlet port and work port, there being no other surfaces of said member exposed to fluid pressure tending to move said member axially, and elastic means biasing said member in a direction tending to close said variable orifice, (b) pressure compensator means for maintaining a constant pressure diflerential between fluid pressures at the inlet port and work port of said variable orifice means, said pressure compensator means including, a body having an inlet port and an outet port, a movable member forming a valve with said body between said inlet port and said outlet port, means defining first and second control chambers, said member presenting opposed control surfaces of equal area to said control chambers and being movable with respect to said body in response to a differential in fluid pressures exerted in said control chambers, said first and second control chambers being the only control chambers pressure in which tends to operate said valve, means constantly exerting a force on said member in a direction tending to close said valve, fluid in said first control chamber being at the pressure of fluid at said inlet port and tending to move said member in a direction opening said valve against the pressure of fluid in said second control chamber, said inlet port communicating with the inlet port of said variable orifice means, said outlet port communicating with the first control chamber'of said variable orifice means, said second control chamber communicating with the work port of said variable orifice means, and (c) a pilot valve having an inlet and an outlet, means including a flow restrictor supplying fluid under pressure to said inlet, a movable valve element cooperable with a control port for establishing a pressure drop between said inlet and said outlet when fluid under pressure is applied to the inlet of said pilot valve, an electromechanical transducer tor actuating said valve element relative to said control port to adjust said pressure drop in accordance with an electric signal applied to said transducer, and passage means applying said pressure drop between said two control chambers of said variable orifice means.

5. Flow control apparatus for maintaining a predetermined rate of flow of fluid under pressure to a work load under variable pressure conditions, comprising, (a) variable orifice means, said variable orifice means comprising a body having a bore therein, an inlet port and an outlet port communicating with said bore at axially spaced positions, a movable valve member slidable in said bore, said member having a fluid passageway centrally formed therein which cooperates with one of said ports to form a variable orifice regulating the flow of fluid from said inlet port to said outlet port through said passageway, the area of said orifice changing as said valve member is moved axially, said member having opposed surfaces of equal areas presented to two opposed pressure control chambers defined in said bore, both said chambcrs being isolated from said passageway, inlet port and outlet port, there being no other surfaces of said member exposed to fluid pressure tending to move said member axially, and a high rate spring biasing said member in a direction tending to close said variable orifice, (b) pressure compensator means maintaining a constant pressure differential between fiuid pressures at the inlet port and outlet port of said variable orifice means, said pressure compensator means including, a body having an inlet port and an outlet port, a movable member forming a valve with said body between said inlet port and said outlet port, means defining first and second control chambers, said member presenting opposed control surfaces of equal area to said control chambers and being movable 'with respect to said body in response to a difierential in fluid pressures exerted solely in said control chambers, a low rate spring urging said member in a direction tending to close said valve, fluid in said first control chamher being at the pres-sure of fluid at said inlet port and tending to move said member in a direction opening said valve against said spring and the pressure of fluid in said second control chamber, said inlet port communicating with the inlet port of said variable orifice means, said outlet port communicating with the first control chamber of said variable orifice means, said second control chamber communicating with the outlet port of said variable orifice means, and (c) an electrically controlled pilot valve for establishing a difierential between the pressures of fluid in the second and first control chambers of said variable orifice means, said pilot valve having an inlet and an outlet, a movable valve element cooperable with a control port for establishing a pressure drop between said control port and said outlet, an electromechanical transducer for actuating said valve element relative to said control port to adjust the magnitude of said pressure drop in accordance with a current applied to said transducer, a fiuid passageway including a flow restrictor communicating between the inlet of said pilot valve and the inlet port of said variable orifice means, a passageway communicating between said control port and said second control chamber of said variable orifice means, and a passageway communicating from the outlet of said pilot valve to the first control chamber of said variable orifice means and a fluid drain, the pressure drop established by said pilot valve and applied between the second and first control chambers of said variable orifice means constituting the only pressure differential acting on the movable member of the variable orifice means tending to vary the area of said orifice, the movable members of said variable orifice means and pressure compensator means being of similar construction and each forming a spool valve with its respective inlet port.

6. Flow control apparatus for maintaining a predetermined rate of flow of fluid under pressure to a work load under variable pressure conditions, comprising, (a) variable "orifice means, said variable orifice means comprising a body having a bore therein, an inlet port and an outlet port communicating with said bore at axially spaced positions, a movable valve member slidable in said bore, said member having a fluid passageway centrally formed therein which cooperates with one of said ports to form a variable orifice regulating the fiow of fluid from said inlet port to said outlet port through said passagewa the area of said orifice changing as said valve member is moved axially, said member having opposed. surfaces of equal areas presented to two opposed pressure control chambers defined in said bore, both said chambers being isolated from said passageway, inlet port and. outlet port, there being no other surfaces of said member exposed to fluid pressure tending to move said member axially, and elastic means biasing said member in a direction tending to close said variable orifice, (b) pressure compensator means maintaining a pressure differential between fluid pressures at said inlet port and outlet port which is substantially constant for any given axial position of said member with respect to said body, and (c) adjustable control valve means for establishing a pressure differential and reflecting said differential between the pressures of fluid in said two control chambers, said control valve means having an inlet connected to the one of said control chambers and an outlet connected to the other of said control chambers, and means including a flow restrictor connecting said inlet to source of pressure fluid, the fiuid force arising from the pressure diiferential established by said control valve means being the sole pressure diflerential fluid force which is exerted on said movable member tending to move said movable member to vary the area of said orifice.

References Cited by the Examiner UNITED STATES PATENTS 1,754,250 4/30 Wright 137-489 2,853,096 9/58 Lee 137-491 2,957,488 10/60 'Farkas 137-117 2,986,161 5/30 Renick 137-501 3,105,671 10/63 Teitelbaum et a1. 25l30 M. CARY NELSON, Primary Examiner.

MARTIN P. SCHWADRON, Examiner. 

1. FLOW CONTROL APPARATUS FOR MAINTAINING A PREDETERMINED RATE OF FLOW OF FLUID UNDER PRESSURE TO A WORK LOAD UNDER VARIABLE PRESSURE CONDITIONS, COMPRISING, (A) VARIABLE ORIFICE MEANS, SAID VARIABLE ORIFICE MEANS COMPRISING A BODY HAVING A BORE THEREIN, AN INLET PORT AND AN OUTLET PORT COMMUNICATING WITH SAID BORE AT SPACED POSITIONS, A MOVABLE VALVE MEMBER SLIDABLE IN SAID BORE, SAID MEMBER HAVING A FLUID PASSAGEWAY CENTRALLY FORMED THEREIN WHICH COOPERATES WITH ONE OF SAID PORTS TO FORM A VARIABLE ORIFICE REGULATING THE FLOW OF FLUID FROM SAID INLET PORT TO SAID OUTLET PORT THROUGH SAID PASSAGEWAY, THE AREA OF SAID ORIFICE CHANGING AS SAID VALVE MEMBER IS MOVED AXIALLY, SAID MEMBER HAVING OPPOSED SURFACES OF EQUAL AREAS PRESENTED TO TWO OPPOSED PRESSURE CONTROL CHAMBERS DEFINED IN SAID BORE, BOTH SAID CHAMBERS BEING ISOLATED FROM SAID PASSAGEWAY, INLET PORT AND OUTLET PORT, THERE BEING NO OTHER SURFACES OF SAID MEMBER EXPOSED TO FLUID PRESSURE TENDING TO MOVE SAID MEMBER AXIALLY, AND ELASTIC MEANS BIASING SAID MEMBER IN A DIRECTION TENDING TO CLOSE SAID VARIABLE ORIFICE, (B) PRESSURE COMPENSATOR MEANS MAINTAINING A PRESSURE DIFFERENTIAL BETWEEN FLUID PRESSURES AT SAID INLET PORT AND OUTLET PORT WHICH IS SUBSTANTIALLY CONSTANT FOR ANY GIVEN POSITION OF SAID MEMBER WITH RESPECT TO SAID BODY, AND (C) ELECTRICALLY CONTROLLABLE MEANS FOR ESTABLISHING A PRESSURE DIFFERENTIAL BETWEEN THE PRESSURES OF FLUID IN SAID TWO CONTROL CHAMBERS, SAID ELECTRICALLY CONTROLLABLE MEANS HAVING AN INLET CONNECTED TO ONE OF SAID CONTROL CHAMBERS AND AN OUTLET CONNECTED TO THE OTHER OF SAID TWO CONTROL CHAMBERS AND TO A FLUID DRAIN, MEANS INCLUDING A FLOW RESTRICTOR CONNECTING SAID INLET TO A SOURCE OF PRESSURE FLUID, THE FLUID FORCE ARISING FROM THE PRESSURE DIFFERENTIAL ESTABLISHED BY SAID ELECTRICALLY CONTROLLABLE MEANS BEING THE SOLE PRESSURE DIFFERENTIAL FLUID FORCE WHICH IS EXERTED ON SAID MOVABLE MEMBER TENDING TO MOVE SAID MOVABLE MEMBER TO VARY THE AREA OF SAID ORIFICE. 